The present invention relates to a method of manufacturing a semiconductor integrated circuit device. More particularly, the present invention relates to a technique that is applicable to a semiconductor integrated circuit device in which two or more types of MISFETs (Metal Insulator Semiconductor Field Effect Transistors) have gate insulating films that are mutually different in thickness and are formed on the same semiconductor substrate.
The operating voltage of a semiconductor device has been reduced generation by generation in the development of semiconductor integrated circuits for achieving higher integration and a lower power consumption. Under such circumstances, a MISFET is reduced in size in accordance with a scaling law for maintaining and improving the device performance, so that the thickness of the gate insulating film is reduced at the same time. However, for example, with a CMOS logic LSI, or the like, the operating voltage is different between the internal circuit and the input/output circuit. For this reason, a MISFET in which the thickness of the gate insulating film is relatively larger is also required.
For such a reason, in a recent semiconductor device, efforts have been pursued to effect the introduction of a process of forming a plurality of types of MISFETs which have gate insulating films that are mutually different in thickness on the same substrate. For example, Japanese Published Unexamined Patent Application No. 2000-188338 discloses a process of separately forming a gate insulating film made of silicon dioxide in a first region of a semiconductor substrate and another gate insulating film made of silicon nitride or tantalum oxide in a second region thereof.